Transparent electrically-conductive layers (TCL) of metal oxides such as indium tin oxide, antimony doped tin oxide, and cadmium stannate (cadmium tin oxide) are commonly used in the manufacture of electrooptical display devices such as liquid crystal display devices (LCD's), electroluminescent display devices, photocells (solar cells), solid-state image sensors, and electrochromic windows. Devices such as flat panel displays have contained a substrate provided with an indium tin oxide layer as a transparent electrode. Such articles can be expensive to make due to the high cost of fabrication. As a result, there has been a strong interest in recent years in making all organic devices comprising plastic resins as flexible substrates and organic electroconductive polymer layers as electrodes. The advantages for such organic devices are significant and they have become the object of considerable research and development efforts worldwide.
Electronically conductive polymers have received considerable attention for the last twenty years in various industries because of their electronic conductivity. Although many of these polymers are colored and less suited for TCL applications, some of the electronically conductive polymers are sufficiently transparent, at least when coated in thin layers on transparent substrates. Descriptions of such electronically conductive polymers are provided, for example relating to substituted and unsubstituted pyrrole-containing polymers in U.S. Pat. Nos. 5,665,498 (Savage et al.) and 5,674,654 (Zumbalyadis et al.), relating to substituted or unsubstituted thiophene-containing polymers in U.S. Pat. Nos. 4,987,042 (Jonas et al.), 4,731,408 (Jasne), 5,300,575 (Jonas et al.), 5,312,681 (Muys et al.), 5,354,613 (Quinters et al.), 5,370,981 (Krafft et al.), 5,372,924 (Quinters et al.), 5,391,472 (Muys et al.), 5,403,467 (Jonas et al.), and 5,443,944 (Azoulay), and EP 440,957A (Jonas et al.) and EP 686,662A (Jonas), and relating to substituted or unsubstituted aniline-containing polymers in U.S. Pat. Nos. 4,070,189 (Kelley et al.), 5,093,439 (Epstein et al.), and 5,716,550 (Gardner et al.).
Many electronic and optical devices are formed using layers of different materials that are stacked on each other. These layers can be patterned to produce the devices. Examples of such devices include optical displays in which each pixel is formed in a patterned array, optical waveguide structures for telecommunications devices, and metal-insulator-metal stacks for semiconductor-based devices. One method for making such devices includes forming one or more layers on a receiver sheet and patterning the layers simultaneously or sequentially to form a device. These methods generally require multiple deposition and patterning steps and can be quite tedious and costly in materials and manufacture. Patterning of such layers is often carried out using photolithographic techniques that can include covering a layer with a photoresist, patterning the photoresist using a mask, removing a portion of the photoresist to expose the underlying layer according to the pattern, and then etching the exposed layer.
The use of wet-etching microlithography to pattern electronically conductive polymers is described for example in WO 97/18944 (Calvert et al.). A similar method is described in U.S. Pat. No. 5,561,030 (Holdcroft et al.) in which a non-conductive prepolymer is patterned and after washing away the mask, the prepolymers is rendered conductive by oxidation. Such methods that use lithographic techniques are cumbersome as they involve many steps and require the use of hazardous chemicals.
The application of electronically conductive polymers in display related devices has been suggested for example in U.S. Pat. No. 5,738,934 (Jones) where the polymers are used as touch screen cover sheets. Electronically conductive polymers are also described for use in liquid crystal display devices but the transparency can be too low.
The use of in-situ polymerized polythiophene and polypyrrole has been proposed in U.S. Patent Application Publication 2003/008135 (Kawamura et al.) as conductive films, for replacement of indium tin oxide. However, such processes are difficult to implement for roll-to-roll production of conductive coatings.
U.S. Pat. Nos. 7,781,047 (Majumdar et al.) and 7,414,313 (Majumdar et al.) describe donor elements useful for transfer of electronically conductive polymers to suitable receiver sheets that can be then used as components in various devices. Polymer transfer is accomplished by the application or heat, pressure, or both and can be in the form of a pattern. Although quite effective for transfer, the conductivity of the transferred layer is limited by that of the electronically conductive polymer, which is often less than metals such as gold or silver. This limited conductivity can reduce the number of uses since many uses require much higher conductivity.
U.S. Pat. No. 7,410,825 (Majumdar et al.) describes a donor laminate that can be used to transfer multiple layers including electronically conductive polymers and a metal to a receiver sheet. The donor laminate includes a substrate and in order, an electronically conductive polymer and a metal layer. After transfer, the receiver sheet then comprises the transferred materials in reverse order. That is, the metal layer is next to the receiver sheet support and the electronically conductive polymer is disposed over the metal layer.
While these donor laminates and transfer method represent an advance in the art because they provide greater conductivity in the resulting articles, the transferred metal layer over the transferred electronically conductive layer can have insufficient transparency. Moreover, the metal layer or grid that is buried under an electronically conductive polymer after transfer may not be as effective an electrical conductor as an exposed metal layer or grid. These problems limit the number of uses of the articles with the transferred layers.